1. Field of the Invention
This invention relates to a method for transferring motion picture images onto a videotape, and more particularly for film to video transfer methods adapted for 3-D television viewing.
2. Description of the Related Art
A new technique for achieving 3-D televisions described in U.S. Pat. No. 4,705,371 to the present inventor. This technique produces a very noticeable 3-D effect by combining a particular type of viewer glasses with a specific filming technique. A moving picture of a scene is recorded such that a relative lateral movement is created between the scene and the recording mechanism. The lateral movement can result from movement within the scene itself, or by moving the camera in various ways. The recorded scene is then viewed through a pair of glasses in which one lens has a greater optical density that the other lens, with the darker lens having a substantially higher transmissivity in the blue region than in the green or yellow regions. The optical density of the darker lens may also be reduced, by increasing its transmissivity, in the red region.
Since this technique avoids the double image inherent in other 3-D television approaches, it has the distinct advantage of presenting a picture which appears to be perfectly clear and natural to an audience which does not have viewer glasses, and yet has a very noticeable 3-D effect when the glasses are worn. However, an optimum picture is not produced when this technique is used in connection with standard film to video transfer techniques.
Moving picture are recorded on silver halide based motion picture film as a sequence of still photographs. Normally 24 or 30 such still photographs or frames per second are recorded to make a motion picture. 24 frames per second has become the standard frame rate for modern motion pictures, and 25 and 30 frames per second have become the standard frame rates for television. Higher frame rates are sometimes used in filming motion pictures, but this is typically for the purpose of achieving a "slow motion" effect.
30 frame television presents 30 complete images per second on the television screen. Each video frame comprises two interleaved fields, with a new field presented each 60th of a second. A motion picture film recorded at 30 frames per second is conventionally transferred to 30 frame per second video by scanning the two interleaved fields of the first video frame from the first film frame. The next two interleaved fields comprising the second video frame are scanned from the second film frame, and so on. To transfer a 24 frame per second film to 30 frame per second video, the first two video fields are scanned from the first film frame, the next three video fields from the second film frame, the next two video fields from the third field frame, and so on.
Television producers often prefer to shoot a program with motion picture film and then transfer the film to videotape, rather than using videotape in the original shoot, because of the much greater dynamic range of motion picture film compared to video cameras. However, when a film to videotape transfer is done and the results viewed through the 3-D viewer glasses disclosed in U.S. Pat. No. 4,705,371, the video images of moving objects appear to jump in steps across the screen as they move. The result is a poor video image quality for moving objects when conventional film to video transfer techniques are used.